extruder positioning problem

hello all

i just build a prusa i3 wth ramps and when i want to start printing

i dont know what happend

i commad it to go to the center of my head bed but it goes on some place near center

FYI:

when i upload marlin frimware i notice that i have to change my enstope direction

should i change anything else??

or some setting in repiter software???

Not much info to go on, please try and upload a video so we can see what's happening. If you say you want it to go to the center, it goes to the center, what is the problem? Is it not moving the amount of mm you expected? In that case you can see if the steps per mm for the x/y axis is correct. Do a search on the reprap.org wiki for setting up the steps per mm.
Triffid Hunter's calibration guide

The printer cannot possibly know where the centre of your bed is. All it knows is the home position (determined by the location of your endstops), the maximum x, y, and z ranges in mm, and also how many steps it needs to turn the motors to produce a mm of travel.

So you just need to go to firmware and enter the correct
#define X_MAX_POS
(and simly for Y and Z)
and
#define DEFAULT_AXIS_STEPS_PER_UNIT
following the guide pointed out above.

It may be that you have already the correct steps/mm, but if your max ranges are not correct then it won't centre where you expect it to.